1. Field of the Invention
This invention relates to a thermosetting resin composition, a prepolymer thereof and a cured product thereof, said composition undergoing curing reaction by heating to proceed stage changes from A stage to B stage and then to C stage and particularly gives a cured product excellent in heat resistance and flexibility.
2. Description of the Prior Art
As resin molding materials having heat resistance of class H, addition polymerization type polyimides such as bismaleimide and the like are well known. This maleimide is often used in combination with a diamine or an epoxy resin. According to the specification of British Pat. No. 1,322,332, a heat-resistant polymer having isomelamine rings was provided by polymerizing a dicyanamide compound, in order to further improve the heat resistance. However, a defect of this polymer is that it is difficult to subject to molding using a usual mold or laminate molding because the polymerization reaction proceeds relatively rapidly. This is because the production of a prepolymer itself is difficult or because even if a prepolymer can be produced, no sufficient fluidity can be retained for the time required for molding because the curing reaction proceeds rapidly.